The present invention relates generally to apparatus for providing a measure of the distance between the apparatus and an object. The apparatus of the present invention has particular importance in the field of distance determining and automatic focusing.
Distance determining and automatic focusing arrangements have received considerable attention in recent years. One advantageous type of distance determining and automatic focusing apparatus is the spatial image correlation type. Examples of the different forms of arrangements of this type can be found in my co-pending application, Ser. No. 627,607, filed Oct. 31, 1975, now U.S. Pat. No. 4,002,899, in my U. S. Pat. Nos. 3,836,772, 3,838,275, and 3,958,117, and in U.S. Pat. No. 3,274,914 by Biederman et al.
The typical spatial image correlation apparatus includes two auxiliary optical elements (e.g. lenses or mirrors) and two detector arrays. The object distance is determined by relatively moving one of the auxiliary optical elements and one of the radiation responsive detector arrays until they occupy a critical or correlation position. This position is a measure of the existing object to apparatus distance.
The relative movement of the auxiliary optical element and the detector array occurs for each distance measuring or focusing operation. The critical condition occurs when there is best correspondence between the radiation distributions of two auxiliary or detection images formed on the two detector arrays. This condition of best distribution correspondence results in a unique value or effect in the processed electrical output signals.
In most systems, the relative movement of the auxiliary optical element with respect to the detector arrays is achieved by moving a lens or mirror relative to one of the detector arrays. The particular position of the element when best distribution correspondence occurs provides a determination of the existing object apparatus distance. In an automatic focusing system, the position of the auxiliary optical element at the time of correlation is used to control the position of a primary optical element, such as a camera taking lens.
Although distance determining and automatic focusing arrangements of this type have many advantages, they also have some disadvantages. In particular, the required movement of an auxiliary optical element and the accurate determination of the position of that element when correlation occurs leads to considerable mechanical and electrical complexity. It also requires some form of motive means to provide the motion of the auxiliary optical element. This can create a problem, particularly in automatic focusing cameras in which size and weight constraints are critical. The additional complexity and the requirement of some form of motive means increases cost as well as weight and size and increases the likelihood of mechanical failure.
In my U.S. Pat. No. 3,945,023, a distance determining and automatic focusing system which does not require a scanning mirror or lens is disclosed. The outputs of detectors in two detector arrays of unequal length are compared and processed to provide an indication of distance to an object. The primary lens is moved to a particular zone depending upon the result of this processing. While this system does not require a scanning mirror or lens, it becomes difficult to implement in practice. In particular, for high accuracy, a relatively large number of zones is required. The signal processing required by this system becomes cumbersome as the number of zones becomes large.